This invention relates to the termination of electrical cables and a method of making a terminal and cable assembly.
Electrical cables are typically comprised of a center electrical conductor that is surrounded by insulation. Conventional crimp-on type electrical terminals have typically been used to provide a connection to the cable. Terminals of this type generally have a first crimp barrel portion which contacts the center electrical conductor and a second crimp barrel portion that attaches around the insulation of a cable. With this type of terminal, the end of the cable must be stripped of its insulation to bare a segment of the electrical conductor before the terminal can be attached. In addition to the insulating material, electrical cables may be comprised of an additional jacketing material which will be stripped and discarded along with the insulation in the conventional stripping operation, thereby adding additional expense.
Because of the processing and material waste costs associated with stripping the ends of a cable in preparation for termination, terminals have been developed that include a crimp barrel portion that attaches around the insulation of a cable and an insulation piercing portion to provide contact with the electrical conductor without stripping the end of the cable. With this type of terminal, material does not have to be stripped from the cable and discarded.
Insulation piercing terminals have found widespread use. However, their use in some applications including the termination of automotive ignition cables has been limited. The reason is that particularly in ignition cable applications, insulation piercing terminals have proven to have inherent reliability problems. A conventional insulation piercing terminal uses sharp edges to cut through the jacket and insulation layers of an electrical cable. The sharp edges make electrical contact with the conductive core of the cable. When the cable assembly is put into use, the sharp edges can lead to high E-field stresses causing burn damage to the conductor. In addition, sharp terminal edges may cut the conductive core which is often comprised of soft non-metallic material. Core cutting or disfigurement can cause arc discharges to occur, which can also lead to conductor burn damage. In addition, inadvertent cutting of the conductive core lowers terminal pull-off forces.
Due to the shortcomings associated with conventional insulation piercing terminals, ignition cables are generally terminated according to a conventional stripping and crimp-barrel type terminal assembly. Therefore, typical termination of an ignition cable involves the process of removing and discarding insulation from the cable.
Once the insulation is removed from an ignition cable the conductive core is typically bent back around the end of the remaining insulation and against the jacket before the terminal barrel is crimped thereover. This type of assembly which includes bending of the conductor is not readily susceptible to application of automated product quality assurance techniques such as vision systems. Therefore, an improvement in the termination of automotive ignition cables will result in better quality control, cost savings and accordingly, is needed. A termination method providing such benefits will additionally lend itself to application in other systems where insulation piercing terminals have proven inadequate or where an improved method of termination is preferred.
When wire wound conductive cores are used in ignition wires the stripping and bending technique has proven difficult. Stripping the insulation from the relatively small diameter conductor can lead to damaging or unraveling the core. This further complicates the termination of ignition cables using conventional techniques.